Resistor thin films formed by low-pressure deposition of molybdenum and tungsten

ABSTRACT

High resistivity, low temperature coefficient of resistance films are formed by evaporating a molybdenum or tungsten source in a low-pressure atmosphere, e.g. 5 X 10 4 torr, of a nitrogen bearing gas, a carbon bearing gas or an inert gas and depositing a resistor film atop a preferably unheated dielectric substrate.

United States Patent Rairden, III Feb. 1, 1972 [54] RESISTOR THIN FILMSFORMED [$6] References Cited LOW-PRESSURE DEPOSITION OF UNI IED STA 1 ESPA'I ENTS MOLYBDENUM AND TUNGSTEN 3,140,460 7/1964 Turkat ..338/308 1lnvemofl J Rflrden, Nlskayunav 3,242,006 3/1966 Gerstenberg........33s/30s x [73] Assigneez General Electric Company 3,258,413 6/1966Pendergast ..204/l92 22 Filed; June 20, 1963 Primary Examiner-William L.Jarvis Attorney-Richard R. Brainard, Paul A. Frank, John J. Kis- [211App]. No.: 738,563 sane, Frank L. Neuhauser, Oscar B. Waddell and MelvinM.

Goldcnberg [52] US. Cl ..ll7/227, 117/107, 204/192, [57] ABSTRACT 338308 [51] Int Cl "01c [7/00 High resistivity, low temperature coefficientof resistance films are formed y evaporating a molybdenum or tungsten[58] FueldoiSearch ..ll7/227, 106 C, 107,204/192, source in a lowmessureatmosphere 5x104 to", of a 338/308 nitrogen bearing gas, a carbonbearing gas or an inert gas and depositing a resistor film atop apreferably unheated dielectric substrate.

12 Claims, 8 Drawing Figures RES/S r/ wry (MICRO Oil/76' c/v) 6'00 1 i ii run/es TEN F/L MS DEPOS/ TED a Y REAC r/ vs EVAPOR/i r/o/v I5 '6mmoaav PRESSURE (MICRO/VS Hg) PAIENTED FEB 1 m2 SHEET 1 BF 4 DEPOS/TIO/V GAS Inventor: dohrv F2. Rdir-den,

AL M tor-nay.

RESISTOR THIN FILMS FORMED BY LOW-PRESSURE DEPOSITION OF MOLYBDENUM ANDTUNGSTEN This invention relates to a method of forming thin filmresistors and in particular to the formation of resistors by the vacuumdeposition of tungsten or molybdenum in an atmosphere of a nitrogenbearing gas, a carbon-bearing gas or an inert gas.

For suitability in sophisticated electronic printed circuitry, thin filmresistor components generally must be characterized by ahigh-resistivity, a low-temperature coefficient of resistance and highlystable electrical properties upon aging. Among techniques heretoforeproposed for forming suitable films are high vacuum depositions oftungsten or molybdenum employing electron beam evaporation and/orsputtering techniques. Similarly, in my copending U.S. application Ser.No. 675,990, filed Oct. 17, 1967, now US. Pat. No. 3,504,325 andassigned to the assignee of the present invention, there is describedand claimed B-tungsten resistor films and the a method of theirformation by the deposition of a vaporized tungsten source undercontrolled environmental conditions of oxygen pressure and substratetemperatures. The formation of resistor thin films by evaporation of aGroup IV or V metal in a nitrogen atmosphere generally is disclosed andclaimed in my copending US. application Ser. No. 670,091, filed Sept.25, 1967 now US. Pat. No. 3,537,891. Notwithstanding the suitablecharacteristics of these thin film resistors for utilization in printedcircuitry, commercial production of resistor films also requires aminimum number of controlled-variables during resistor film formation tolower fabrication costs. Many presently employed commercial methods ofresistor film formation however require sophisticated apparatus formaintaining the substrate at a precise elevated temperature duringeither the deposition or the subsequent appealing of the deposited filmto obtain suitable resistor characteristics.

It is therefore an object of this invention to provide a novel method offorming tungsten and molybdenum resistor films having high-resistivity,low-temperature coefficient of resistance and good stability upon aging.

It is also an object of this invention to provide an economical methodof constructing tungsten and molybdenum resistor films havingcharacteristics suitable for printed circuitry.

it is a further object of this invention to provide a method of formingtungsten and molybdenum resistor films having good stability withoutpost deposition aging treatments.

These and other objects of this invention generally are achieved bypositioning a dielectric substrate and a source material selected fromthe group consisting of molybdenum and tungsten within an evaporationchamber which chamber,

after evacuation, is filled with a gas selected from the groupconsisting of the nitrogen bearing gases, the carbon bearing gases andthe inert gases in sufficient quantities to produce a source tosubstrate distance-pressure arithmetic product greater than 355x torrcentimeters. The source then is vaporized by any suitable technique,e.g., electron beam evaporation, and a resistor film is deposited uponthe substrate. In general, highest resistivity films for a fixeddeposition pressure are obtained when the substrate is unheated, withsuitable tungsten films being obtainable to a maximum substratetemperature of approximately 455 C. and suitable molybdenum films beingobtainable to a maximum substrate temperature of 155 C.

The novel features believed characteristic of the invention are setforth in the appended claims. The invention itself, together withfurther objects and advantages thereof may best be understood byreference to the following description, taken in connection with theaccompanying drawings, in which:

HO. 1 is a schematic view of apparatus suitable for forming resistorfilms in accordance with this invention,

HO. 2 is a graph depicting the variation of resistivity with pressurefor various substrate temperatures during tungsten depositions,

HO. 3 is a graph depicting the variation of temperature coefficient ofresistance with resistivity for resistor films formed by tungstendepositions,

FIG. 4 is a graph depicting the variation of temperature coefficient ofresistance with film resistance for films formed by tungsten depositionsin accordance with this invention,

FIG. 5 is a graph depicting the aging characteristics of tungstenresistor films,

FIG. 6 is a graph depicting the variation of resistivity with pressurefor various substrate temperatures during molybdenum depositions,

FIG. 7 is a graph depicting the variation of temperature coefficient ofresistance with resistivity for resistor films formed by molybdenumdeposition in accordance with this invention, and

FIG. 8 is a graph depicting the variation of temperature coefficient ofresistance with resistance for films formed by molybdenum depositions inaccordance with this invention.

Apparatus suitable for forming resistor films in accordance with thisinvention is depicted in FIG. 1 and generally includes an evaporationchamber 10 having a transverse electron beam gun 11 positioned thereinfor evaporation of a portion of a source material 12, e.g., a metalselected from the group consisting of tungsten and molybdenum,positioned within cup 13 of a water cooled crucible 14. The evaporatedsource then passes through the controlled gaseous environment within thechamber and is deposited to a thickness less than 10,000 A. uponsubstrate 15 to form a high resistivity, low temperature coefficient ofresistance film.

Evaporation chamber 10 is conventional in structure and generallyincludes a stainless steel envelope 17 positioned atop a circular base18 with a suitable sealant, shown as gasket 19, being provided betweenenvelope [7 and base 18 to assure isolation of the evaporation chamberinterior. Evacuation of the chamber is accomplished through an aperture20 approximately centrally positioned within base 18 and communicated toexhaust pump 21 by exhaust lines 22 and 23. A liquid nitrogen trap 24 ispositioned intermediate exhaust lines 22 and 23 to prevent contaminationof the chamber by a backfeed through the exhaust lines during evacuationof chamber 10. g

A second aperture 25 within base 18 permits the admission of a suitabledeposition atmosphere, e.g a gas such as nitrogen, ammonia, methane,carbon monoxide, carbon dioxide, argon, or neon, into the chamberthrough conduit 28 and motor driven variable leak valve 29 tocontinuously maintain the gaseous pressure within the evaporationchamber at a desired level (as will be explained hereinafter) for theformation of high-resistivity, low-temperature coefficient resistancefilms. An ionization gauge 30 positioned within the enclosed chamber andcommunicated to automatic valve controller 31 through electrical lead 32functions to control the operation of variable leak valve 29 andregulate the gaseous pressure within chamber 10.

Substrate 15, upon which the resistor film is to be deposited, can beany suitable nonconductive material, e.g., soda lime glass quartz, mica,or aluminum oxide, and is seated within a rectangular frame 33positioned at the upper end of an angularly shaped stantion 34protruding upwardly from base 18. To pennit heating (when desired) ofthe substrate during deposition, a tungsten heater coil 35 is situatedin an overlying attitude relative to the substrate and is energized byan alternating current source 37 through disconnect device 38. A heatreflector 40 shrouds tungsten heater coil 35 to concentrate thegenerated heat from the coil upon the surface of the substrate and aplatinum/platinum rhodium thermocouple 41, connected to a temperaturegauge 42 through electrical lead 43, is positioned along the edge of thesubstrate face remote from the source 12 to permit visual monitoring ofthe substrate temperature. A suitably apertured shield 44 is positionedin a generally underlying attitude relative to the substrate to limitthe film deposition area to a suitable size, e.g., l mm. by 10 mm. (10square), thereby permitting simplified film resistance measurements byconventional methods such as the fourprobe technique.

The transverse electron gun ll utilized for evaporation of source 12generally includes a cathode 47 energized by a negative DC potential 46through leads 36 for the emission of electrons and a grounded anode 48having an oval aperture 49 through which the generated electrons arepropelled as a stream. As the generated electron stream passes beyondanode 48, the magnetic field produced by a pair of generally upstanding,slightly convergent pole pieces 26 deflects the electrons in an arcuateattitude to impinge the electron stream upon source 12 therebyevaporating a portion of the source. Energization of cathode 47 with aDC potential of 7.5 kilovolts and a generation of a 700 milliamperestream from the electrode has been found to provide sufficientevaporation of the source to deposit 245 A. per minute upon a substratepositioned approximately 35.5 cm. from the source.

In the operation of the method of this invention a suitablenonconductive substrate such as a soda lime glass substrate, after beingsuitably cleaned, is seated within rectangular frame 33 and a sourcematerial selected from the group consisting of tungsten and molybdenumis positioned within cup 13 of water cooled crucible 14 at asuitabledistance, e.g., 35.5 cm., from the substrate. Stainless steelenvelope 17 then is placed upon circular base l8 and exhaust pump 21 isoperated to evacuate the chamber to a relatively low pressure ofapproximately X10" torr. Upon evacuation of the chamber, variable leakvalve 29 is operated to' purge the system for a suitable period, e.g.,minutes, with the gas selected to be employed during the evaporation andthe pressure in the chamber is regulated relative to the source tosubstrate distance to produce a source to substrate distance'gaspressure arithmetic produce between 35.5 10 torr cm. to 35.5 10 torrem., e.g., a gaseous level between 1X10 torr to l 10- torr for a 35.5cm. source to substrate distance. Electron beam gun ll then is energizedto evaporate the chosen source in sufficient example, 300 A. per minute,upon a preferably unheated substrate (as will be more fully explainedhereinafter); Upon deposition of a film of a desired resistance, e.g.,to a thickness less than 10,000 A., vaporization of the source isterminated and the film is allowed to cool in the deposition gasatmosphere. Although either nitrogen bearing gases, e.g., nitrogen orammonia; carbon-bearing gases, e.g., carbon monoxide, carbon dioxide,methane etc.; or inert gases, e.g., argon, neon, etc., can be employedas the deposition gas utilizing the method of this invention, nitrogenis preferred because resistor films deposited therein exhibit asubstantially higher resistivity than resistor films deposited undersimilar conditions in other gaseous atmospheres contemplated by thisinvention. For example, an approximately 900 A. tungsten film depositedupon a room temperature substrate in an argon pressure of 8X10 torrexhibited a resistivity of 1,040 u ohmcm. and an 813 A. tungsten filmidentically deposited in an ammonia atmosphere exhibited a resistivityof 1,028 u ohmcm. while a slightly thicker, e.g., 1,473 A. tungsten filmdeposited in a nitrogen atmosphere under otherwise identical conditionsexhibited a substantially higher resistivity of 2,290 a ohm-cm.

As can be noted from the graph of FIG. 2 depicting the variation ofresistivity with pressure for resistor films formed by electron beamevaporation of tungsten in a nitrogen atmosphere utilizing a 35.5 cm.source to substrate span, increasing deposition pressures produce anincrease in the measured resistivity of the deposited resistor films.For example, an increase in pressure from 0.l 10- torr to 0.8 10 torrnitrogen generally effected approximately a doubling in the measuredresistivity of the tungsten resistor films deposited under otherwiseidentical conditions. To obtain extremely high film resistivities, e.g.,above 1,000 p. ohm-cm., a deposition pressure above approximately0.4X10' torr is required for the 35.5 cm. source to substrate span,e.g., a source to substrate-pressure arithmetic product above 14.2)(10torr cm. Because the mean free path of a molecule, e.g., the averagetravel distance required for a vaporized tungsten molecule to collidewith a gaseous molecule within the evaporation chamber, is characterizedby a source to substrate-pressure arithmetic product of at least 5X10torr cm., high-resistivity tungsten films only are obtained when one ormore collisions occur between the evaporated tungsten and gaseousdeposition atmosphere prior to the deposition of the film upon thesubstrate. Although the upper limitof the pressure range employed forforming films by the method of this invention generally is limitedprimarily by the apparatus utilized for deposition, e.g., electron beamapparatus tends to become inoperative at pressures in excess of about2X10 torr, an inordinate number of collisions, e.g., 10 or more, betweenthe vaporized metal and the gas within the chamber can result in poorcontinuity and adhesion of the deposited material.

While the graph of FIG. 2 shows the variation of resistivity withpressure for a 35.5 cm. source to substrate distance, it is to berealized that extremely high measured resistivities of the depositedfilm are obtained by the controlled interaction (or collision) of theevaporated metallic source molecules with the deposition gas within thechamber and therefore are not limited to the specific pressures of FIG.2. For example, a tungsten source evaporated in a nitrogen pressure of4X10 torr utilizing a 17.71 cm. source to substrate distance anddeposited at 300 A. per minute upon a glass substrate exhibited ameasured resistivity of 545 [L ohm-cm. (well above the bulk resistivityof tungsten) and a temperature coefficient of resistance of 105p.p.m./C.

When different source to substrate distances are employed fordeposition, the deposition gas pressure within the chamber is altered toassure a desired number of collisions between the evaporated source andthe deposition gas to obtain the high measured resistivity in the film.For example, as the mean free path of the evaporated source molecule isdecreased by an increase in the deposition gas pressure, the source tosubstrate distance is decreased to assure a similar interaction betweenthe evaporated source molecules and the gaseous atmosphere prior todeposition upon the substrate. As a practical matter however, source tosubstrate spans between 125 cm. and 9 cm. are required for vacuumevaporation of high resistivity films. In general, elongated source tosubstrate spans permit a more uniform coating upon a larger substratearea. The lower deposition pressures associated with the elongatedsource to substrate spans however can tend to accentuate the presence ofbackground gases, e.g., gases other than the deposition gas, within thedeposition chamber tending to slightly alter the resistor filmcharacteristics. Highest resistivity films were obtained utilizing asource to substrate span greater than 20 cm.

Notwithstanding the desirability of a relatively high gaseous pressureduring the tungsten deposition to assure sufficient collisions for theformation of high resistivity films, x-ray analysis of selected highresistivity films of this invention indicate the films to be fi-tungstenrather than a tungsten nitride or a tungsten carbide. It is thereforepostulated that all the various gaseous atmospheres employed duringdeposition serve to produce interstitual impurities in the depositedfilms to substantially increase the resistivity in the deposited filmsrelative to the resistivity of bulk tungsten while the more activegases,

such as nitrogen and methane, chemically react" with the evaporatedtungsten to form extremely high resistivity B-tu ngsten films.

As can also be seen from the graph of FIG. 2 the resistivity of tungstenfilms deposited at a given pressure varies inversely with the substratetemperature during deposition with highest resistance films being formedupon substrates at room tem' pcrature. When substrate temperatures above455 C. are employed, a conventional a-tungsten film is deposited ratherthan the B-tungsten structure required for extremely high resistivityfilms. Films deposited on substrates maintained at a temperature ofapproximately 240 C. exhibit both B-tungsten and a-tungstencharacteristics. Thus to obtain high resistivity films, the substrateshould be maintained at a temperature below at least 455 C. duringdeposition and preferably below 240' C. Because films deposited uponunheated substrates produce the highest resistivity and generallyrequire no regulation of the substrate temperature thereby minimizingfabrication costs, the formation of films upon unheated substrates ispreferred.

Referring more particularly to FIG. 3, tungsten films formed by themethod of this invention can approach a resistivity of approximately1,100 1 ohm-cm. before the temperature coefficient of resistance of thefilm exceeds -50 p.p.m./ C. when temperature cycled between 25 C. and125 C. Furthermore because the temperature coefficient of resistancecurve of FIG. 3 is relatively flat, films having similar temperaturecoefficients of resistance can be formed over a wide range ofresistivity; e.g., resistor films having a temperature coefficient ofresistance within :25 p.p.m./ C. are capable of exhibiting resistivitiesvarying from approximately 450 ,u ohm-cm. to 850 .t ohm-cm.

Tungsten films formed by the method of this invention also arecharacterized by an extremely high resistance for a generally tolerabletemperature coefficient of resistance, e.g., a temperature coefficientof resistance less than 200 p.p.m./ C. As illustrated in FIG. 4,tungsten films having resistances above 2,000 ohms per square have beenobtained with a temperature coefficient of resistance of less than 1 50p.p.m./ C.

The deposition rate employed in the formation of the resistor films ofthis invention generally has been found not to be extremely criticalwith high resistivity tungsten films being formed at deposition ratesbetween 50 to 1,000 A. per minute. While the deposition rate does havesome effect on the characteristics of the films formed, e.g., lowerdeposition rates generally tend to produce higher resistivity films, theeffect of deposition rate on film characteristics is minimal comparedwith the effect produced by variations in either the substratetemperature and the pressure employed during the film deposition.

Extremely thin tungsten resistor films, e.g., films having a resistanceabove 1,500 ohms per square,- generally exhibit an unstable agingcharacteristic, as is shown in FIG. 5. Thus when tungsten resistor filmshaving a high resistance are desired, protective coatings, such assilicon monoxide, should be deposited atop the resistor film prior tothe admission of atmospheric gases into deposition chamber to inhibitaging of the resistor film. Because extremely thick tungsten films cantend to crack glass substrates due to stresses induced in the filmduring deposition and due to the difference in coefficient of thermalexpansion of the film and underlying substrate, preferably the resistorfilms are deposited to a thickness less than 10,000 A.

Molybdenum films generally exhibit a resistivity which varies with thenitrogen deposition pressure in a manner similar to that of tungsten,e.g., a rising resistivity for increasing nitrogen pressure, as can beseen from FIG. 6 wherein resistivity variation with nitrogen pressure isdepicted for molybdenum depositions employing a source to substratedistance of approximately 35.5 cm. Thus, the source to substratedeposition gas pressure arithmetic product required for the formation ofhigh resistivity molybdenum films generally is in excess of 3.6Xl0 torrcm. with molybdenum films exhibiting resistivities above 350 ,uohm-cm.being formed only at gaseous pressures greater than the mean free pathof the vaporized molybdenum molecule, e.g., greater than 0.15 micronsnitrogen pressure in the graph of FIG. 6.

The resistivities of molybdenum films deposited in accordance with thisinvention generally vary inversely with the substrate temperatureemployed during deposition with relatively high-resistivity molybdenumfilms being formed upon substrates at approximately 25 C. As illustratedin FIG. 6, the resistivity of the deposited molybdenum films dropsrapidly with increasing substrate temperature and high-resistivity filmsare formed only when the substrate is maintained at a temperature ofless than 150 C. during deposition. The extreme dependency of themolybdenum resistor characteristics upon substrate temperature wasexemplified by the deposition of three molybdenum film samples underidentical conditions except for a variation in substrate temperature.The molybdenum film deposited at room temperature exhibited aresistivity of approximately 1,740 n. ohm-cm. and a temperaturecoefficient of resistance of approximately 0 p.p.m./ C. while themolybdenum resistor films deposited at temperatures of 205 C. and 465 C.exhibited decreasing resistivities of 425 uohm-cm. and 27 #ohm-cm,respectively.

As can be seen from the graph of FIG. 7, the temperature coefficient ofresistance of the deposited molybdenum films when temperature cycledbetween 25 C. and C. asymptomatically approaches a level ofapproximately less than +50 p.p.m./ C. for nitrogen pressures above 0.6microns utilizing a 35.5 cm. source to substrate span. Thus, molybdenumdepositions at relatively high pressure, e.g., a source to substrate-gaspressure arithmetic product above 2l.3 l0 torr centimeters, generallyproduce films having a low temperature coefficient resistance, e.g.,less than +50 p.p.m./ C. and a high measured resistivity, e.g., above1,000 zohm-cm. for an unheated substrate. Ascan be seen however from acomparison of FIGS. 4 and 8, films formed by molybdenum depositionsgenerally are characterized by a slightly lower resistance for a giventemperature coefficient of resistance than tungsten films similarlyformed. For example, while tungsten films exhibit a temperaturecoefficient of resistance less than -l00 p.p.m./" C. up to approximately1,100 ohms per square, molybdenum films exhibit a temperaturecoefficient of resistance of l00 p.p.m./ C. only up to approximately 900ohms per square.

A more complete understanding of the principles of this in vention canbe obtained from the following specific examples of resistor filmdepositions employing various sources and deposition gases.

EXAMPLE 1 After a soda lime glass microscopic slide was cleaned byboiling in water containing detergent, rinsing in cold then hotdeiodized water, rinsing in isopropyl alcohol and drying in isopropylalcohol vapors, the substrate was placed in a stainless steel framelocated approximately 35.5 cm. from a tungsten source in an evaporatorchamber. The chamber then was evacuated to a pressure of approximately5X10 torr whereupon nitrogen was admitted into the chamber to purge thechamber for approximately 10 minutes. After purging, the chamber wassealed, the pressure in the chamber raised to 8 l Otorr nitrogen and theelectron beam gun employed for evaporation of the tungsten sourceenergized with sufficient power to produce a deposition rate ofapproximately 275 A. per minute upon the glass substrate. Deposition wascontinued for approximately 320 seconds to produce a resistor filmhaving a thickness of about 1,473 A. After the deposited film was cooledin the nitrogen atmosphere of the deposition chamber, subsequentmeasurement of the resistance characteristics of the deposited filmemploying the conventional four probe" technique indicated theresistivity of the film to be 2,290 ,uohm-cm. while temperature cyclingof the resistor film from 25 C. to 125 C. indicated the film to have atemperature coefficient of resistance of l 20 p.p.m./ C.

EXAMPLE 2 A soda lime glass substrate was cleaned as in the previousexample and placed within a stainless steel holder 35.5 cm. from atungsten source in a vacuum chamber. The substrate then was preheated to295 C. during the evacuation of the chamber to a pressure ofapproximately 5X10 torr whereupon the chamber was purged with methanefor 15 minutes, during which period the substrate heating was reduced to280 C. After purging and sealing the chamber, the methane pressurewithin the chamber was set at 8X10 torr and the electron beam gunenergized to vaporize the tungsten in sufficient quantities to produce adeposition rate of approximately 360 A. per minute upon the substrate.Deposition was continued for 12 minutes to produce a resistor film ofapproximately 4,500 A. upon the substrate and the substrate wasmaintained at 280 C. for 15 minutes in the methane atmosphere of thechamber subsequent to the deposition. After cooling in the methaneatmosphere, subsequent measurement of the tungsten film disclosed ameasured resistivity of 386 p. ohm-cm. and a temperature coefficient ofresistance of +78 p.p.m./ C. when cycled between 25 C. and 125 C EXAMPLE3 Deposition techniques identicalto that of example 1 were employedexcept for the fact that ammonia was utilized as the gaseous mediumwithin the chamber during deposition and the deposition was conductedfor a period of 220 seconds to produce a film of 813 A. Subsequentresistance measurements of the film indicated the film to have ameasured resistivity of 1,028 z ohm-cm. and a temperature coefficient ofresistance of -l 60 p.p.m./ C. when cycled between 25 C. and 125 C.

EXAMPLE 4 An approximately 893 A. resistor film was deposited in an8X10torr argon atmosphere under conditions otherwise identical to thoseof example 3. Subsequent resistance measurements indicated the depositedfilm to have a measured re-' sistivity of 1,040 p. ohm-cm. and atemperature coefficient of resistance of l20'p.p.m./C. when cycledbetween 25 C. and 125C.

EXAMPLE 5 source then was initiated at a sufficient power level toproduce a deposition rate of 265 A. per minute for approximately 3minutes thereby forming a film approximately 789 A. thick.

,Sub'sequent measurements of the film characteristics indicated the filmto have a measured resistivity of 1,170 1. ohmcm. and a temperaturecoefficient of resistance of -30 p.p.m./ C. when cycled between 25 C.and 125 C.

EXAMPLE 6 A molybdenum source was placed within an evaporation chamberat a span of 35.5 cm. from a clean glass substrate and the chamberfilled with methane to a pressure of 8X10" torr after an initial exhaustand a purge for approximately 10 minutes with methane gas. Uponenergization of the electron beam source, a film was deposited at a rateof approximately 885 A. per minute for seconds to form a 295 A. thickfilm upon the substrate. Subsequent resistance measurements of the filmindicated the film to have a resistivity of 337 ,u. ohmcm. and atemperature coefficient of resistance of +130 p.p.m./ C. when cycledbetween C. and 125 C. The resistance of the deposited film measuredapproximately 1,070 ohms/sq.

EXAMPLE 7 This example was conducted in a manner identical to example 5except for the employment of ammonia gas as the atmosphere within thechamber. The molybdenum source was evaporated at a rate of 935 A. perminute for 70 seconds to produce a 1,090 A. thick film. Subsequentmeasurements of the resistive characteristics of the film indicated ameasured resistivity of 2,580 ptohm-cm, a temperature coefficient ofresistance of -290 p.p.rn./ C. when cycled between 25 C. and 125 C., anda resistance of 2,300 ohms/sq.

While the invention has been described with respect to certain specificembodiments, it will be appreciated that many modifications and changesmay be made without departing from the spirit of the invention. Iintend, therefore, by the appended claims, to cover all suchmodifications and changes as fall within the true spirit and scope of myinvention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. A method of forming high-resistivity, low-temperature coefficient ofresistance films comprising the steps of:

positioning a dielectric substrate and a source material from 9 tocentimeters apart within an evaporation chamber; selecting said sourcematerial from the group consisting of molybdenum and tungsten;evacuating said chamber; introducing a deposition gas into said chamberto produce a working pressure within said chamber of from 1X10 to 1 X 1Otorr; selecting said deposition gas from the group consisting ofnitrogen bearing gases, carbon-bearing gases and inert gases; vaporizingat least a portion of said source material; and depositing a resistorfilm upon said substrate. 2. A method of forming high-resistivity,low-temperature coefficient resistance films according to claim 1wherein said source is tungsten and said substrate is maintained at atem-' perature less than 370 C. during deposition. I

3. A method of forming high-resistivity, low-temperature coefficientresistance films according to claim 1 wherein deposition gas is selectedfrom the group consisting of nitrogen, methane, ammonia, and argon.

4. A method of forming high-resistivity, low-temperature coefficientresistance films according to claim 3 wherein said deposition gas isnitrogen, and said source is evaporated by electron beam evaporation.

5. A resistor film formed by the method of claim 3.

6. A method of forming high-resistivity, low-temperature coefficientresistance films according to claim 1 wherein said source is molybdenumand said substrate is maintained at a temperature less than C. duringdeposition.

'7. A method offorming high-resistivity low-temperature coefficientresistance films according to claim 6 wherein said deposition gas isnitrogen, and said source is evaporated by electron beam evaporation.

8. A resistor film formed by the method of claim 7. 9. A method offorming high-resistivity, low-temperature coefficient of resistancefilms comprising the steps of:

positioning a dielectric substrate a predetermined distance from asource selected from the group consisting of molybdenum and tungstenwithin an evacuation chamber, wherein said predetermined distance isfrom 9 to 125 centimeters,

evacuating said chamber and introducing a deposition gas selected fromthe group consisting of nitrogen, ammonia and methane into said chamberto produce a pressure of from 1X10 to 1X10 torr to effect at least onecollision between a vaporized source molecule and a gaseous moleculeprior to deposition of vaporized material from said source upon saidsubstrate,

vaporizing said source, and

depositing a resistor film upon said substrate to a thickness less than10,000 A.

10. A method of forming high-resistivity, low-temperature coefficient ofresistance films according to claim 9 wherein said substrate ismaintained in a temperature less than approximately 50 C. during saiddeposition.

11. A method of forming high-resistivity, low-temperature coefficient ofresistance films according to Claim 10 wherein said source is tungstenand said film is deposited in a nitrogen atmosphere to a thicknessproducing a resistance less than 5X10ohms per square.

12. A method of forming high-resistivity, low-temperature coefficient ofresistance films according to Claim 10 wherein said deposition gaspressure within said chamber is set relative to said source to substratedistance to effect a plurality of collisions between a vaporized sourcemolecule and a gas molecule prior to deposition.

2. A method of forming high-resistivity, low-temperature coefficientresistance films according to claim 1 wherein said source is tungstenand said substrate is maintained at a temperature less than 370* C.during deposition.
 3. A method of forming high-resistivity,low-temperature coefficient resistance films according to claim 1wherein deposition gas is selected from the group consisting ofnitrogen, methane, ammonia, and argon.
 4. A method of forminghigh-resistivity, low-temperature coefficient resistance films accordingto claim 3 wherein said deposition gas is nitrogen, and said source isevaporated by electron beam evaporation.
 5. A resistor film formed bythe method of claim
 3. 6. A method of forming high-resistivity,low-temperature coefficient resistance films according to claim 1wherein said source is molybdenum and said substrate is maintained at atemperature less than 150* C. during deposition.
 7. A method of forminghigh-resistivity low-temperature coefficient resistance films accordingto claim 6 wherein said deposition gas is nitrogen, and said source isevaporated by electron beam evaporation.
 8. A resistor film formed bythe method of claim
 7. 9. A method of forming high-resistivity,low-temperature coefficient of resistance films comprising the steps of:positioning a dielectric substrate a predetermined distance from asource selected from the group consisting of molybdenum and tungstenwithin an evacuation chamber, wherein said predetermined distance isfrom 9 to 125 centimeters, evacuating said chamber and introducing adeposition gas selected from the group consisting of nitrogen, ammoniaand methane into said chamber to produce a pressure of from 1 X 10 3 to1 X 10 4 torr to effect at least one collision between a vaporizedsource molecule and a gaseous molecule prior to deposition of vaporizedmaterial from said source upon said substrate, vaporizing said source,and depositing a resistor film upon said substrate to a thickness lessthan 10,000 A.
 10. A method of forming high-resistivity, low-temperaturecoefficient of resistance films according to claim 9 wherein saidsubstrate is maintained in a temperature less than approximately 50* C.during said deposition.
 11. A method of forming high-resistivity,low-temperature coefficient of resistance films according to Claim 10wherein said source is tungsten and said film is deposited in a nitrogenatmosphere to a thickness producing a resistance less than 5 X 10 3 ohmsper square.
 12. A method of forming high-resistivity, low-temperaturecoefficient of resistance films according to Claim 10 wherein saiddeposition gas pressure within said chamber is set relative to saidsource to substrate distance to effect a plurality of collisions betweena vaporized source molecule and a gas molecule prior to deposition.